Potentiometers



March l0, 1964 R. E. CADDocK ETAL 3,124,779

POTENTIOMETERS Filed Nov. 14. 1960 MAR/ AN E. BauR/vs 12a BY f i] ,20 /0 4 128 [24 v f United States Patent O 3,124,779 POTENTIOMETERS Richard E. Caddock, Riverside, Calif., and Marian E.

Bouma', 2530 Piedmont Drive, Riverside, Calif.; said Caddock assignor to Boul-us, Inc., a corporation of Califomia Filed Nov. 14, 1960, Ser. No. 69,060 20 Claims. (Cl. 338-180) This invention relate-s to new and improved variable esistors such as potentiometers; :and is a continuation-in- )art of application Ser. No. 743,308 tiled bythe inventors iereof on June 20, 1958.

At the present time potentiometers of one type are manufactured so as to include a hou-sing within which here is mounted a resistance element :and a threaded haft extending parallel to the resistance element. In nstuuments of that type a contact .device is moved by he shaft as the shaft is turned, the contact device movug along the length of the resistance element and estabishing an electrical connection between the element and .part of the potentiometer serving as an electrical return. n some pctentiometers of that type the shatit itself is mployed as the electrical return; in others, a separate onductor is employed `as an electrical return or shorting trip.

Some potentiometers ot the type brieily ldescribed in the receding paragraph are manuactured lso as to be of Omparatively small size. As la result of this miniaturizaion a number of problems are encountered in manufacuring at a reasonable cost instruments which are capable if withstand-ing normal abuse incident to handling, intall-ation and use. Typical of the types of abuse that nay occur is that occurring when an operator turns the hreaded shaft employed in this type of potentiometer too ar in either direction and thereby causes the contact evice to travel too ar and press against either of the nds of the unit. Such operation or excessive shaft rotaon will tend to strip the threads connecting the shaft lith the contact device. When this occurs the poteniometer is damaged to such `an extent that its utility is npaired if not completely destroyed.

A broad object of the present invention is to provide new type of contact device for use in potentiometers. /Iore specifically it is a bro-ad object of this invention 3 provide a new type of contact device which ovencomes isadvantages and limitations of prior types of variable esistor contact devices. In accordance with the broad eachings of this invention, these general objects are chieved through the use ot a contact device or means Ihich has a groove that is disposed against one side off threaded shaft, anda spring-like element extending over 1e shaft so as to hold the device and shaft together with 1e shaft positioned in the groove. The spring-like eletent is formed so as to resiliently engage the thread of 1e shaft. The construction and arrangement or the pringlike element is such that it is capable of moving r snapping over the thread on the shaft when the matt has been turned to yan extent such as to force the ontact device against some obstruction such as, :for xamzple, an end of a housing lin which the parts are disosed.

Another object of the present invention -is to provide a ew tylpe of potentiometer construction in which a contct device is :formed entirely of metal and in which the ontact device electrically interconnects the threaded letal shaft of the potentiometer with the resistance eleient employed.

A further object is to provide in this type of instrulent a spring-like shaftretaining clip which serves as a 3,124,779 Patented Mar. 10, 1964 terminal for the shaft used as an electr-ical return. Another object of the present invention is to provide a new `type of terminal construction `for use with resistance elements such as may be employed in potentiometers.

Another object of the present invention is to provide a new type ot contact device as described in .the preceding paragraphs in which Contact member a groove is for-med in a non-conductive body member and in which device separate spring means are employed so as to resil-iently engage a threaded shaft as herein indicated. With this type of contact device construction the complete device includes Contact means 'which are attached to Aa body member, and which contact means extend from the body memiber so as -to engage a resistance element and la return conductor. Another `object of the present invention is to provide in po-tentiometers a new and improved construction for securing a resistance element in place.

Additional objects and advantages of the invention will become fully app-arent t-o those skilled in the art to which this invention pertains from a detailed consideration of the remainder of this specification, including the appended claims and the accompanying drawing in which:

FIG. l is a perspective View of `a potentiometer according .to this invention;

FIG. 2 is a cross-sectional view taken as .indicated by line 2 2` of FIG. l;

FEG. 3 is a cross-sectional View taken yas indicated by line 3 3 of FIG. 2;

FIG. 4 is a partial cross-sectional view taken 'as indicated by line 4 4 of FIG. 2;

FIG. 5 is a perspective view illustrating a contact device employed in the potentiometer illustrated in the previously described figures;

FIG. 6 is a partial cross-sectional view taken on a plane indicated by line 6-6 of FIG. 2;

FIG. 7 is a vi-ew similar to FIG. 2, depicting in partial section a modi-tied form of potentiometer according to this invention;

FIG. 8 is a partial oross-sectional view taken as indicated by line 8 8 of FlG. 7; and

FIGS. 9 and 10 `are perspective views of parts employed in the potentiometer illustrated in partial section in FIG. 7.

In all gures of the dnawing like numerals are u-sed to designate like pants wherever convenient for purposes of iilustration and explanation. It is to be understood that the accompanying drawing is primarily intended to designate certain presently preferred embodiments or forms of this invention. Those skilled in the a-nt to which the present invention pertains will realize that a number of differently-appearing electrical instruments may be manufactured so .as to utilize one or more features of the complete inventive concept set forth in this specification.

In order to explain the present invention more t'ully reference is made to the :accompanying drawing. In FIGS. 1, 2 and 3 oi the drawing, there is shown a complete potentiometer according to the present invention, which potentiometer includes two substantially symmetrical housing sections 12 formed ot a phenolic resin or other similar non-conductive compositi-on. These two sections are adapted to be secured together as shown and are so shaped or formed as to define within the potentiometer 10 an elongate cavity 14 having ends 16 and 18 and to :define various other passages and :cavities as hereinafter described. The two sections 12 are assembled and secured together by mean-s hereinafter described, to form a body or housing. Therein, a complete resistance element 20 having a nonconductive mandrel 22- is located with its ends held in sockets 214` formed by complementary depressions produced in the sections i12, the sockets being situated in [the .ends 16 and 18 of the cavity 14, as indicated in FIG. 2. Resistance wire 26 is wound over` the mandrel 22, and lat the ends of the element are terminals 28. Each of the terminals 28 has a ring-shaped end portion 30 (FIG. 4), which encircles the wire windings at the end of vthe element to make electrical contact therewith. Notches 34 in the terminals 218 fit ove-r projections 32 in small passages leading from the cavity 14 to the outside of the potentiometer 10, `so as to Klock these tenminals in place.

A metal shaft, or leadscrew 38, formed as indicated, is carried in openings 40 and 42 formed in the housing at respective ends 16 and 18 of the cavity 14, the leadscrew extending in cavity 14 parallel to the resistance element 20. Shoulder or abutment means, here shown in the form of a radial flange 44, is formed on the shaft near the right-hand end thereof, and this flange 44 is located within a smaller cavity 46 defined by opposed depressions produced in respective ones of the housing sections 12. The flange 44 bears against a complementary abutment 47 provided in one or both of sections 12 which abutment 47 faces toward the right-hand end of the body, as seen in FIG. 2 so as to position the leadscrew 38 within the body and prevent endwise movement of the leadscrew toward the opposite end of the body. The right-hand end of the leadscrew or shaft 38 is provided with a atsided portion 48 which is slidably received within a correspondingly shaped cavity 58 in a non-conductive head 52 The head 52 may be formed of plastic such as a hardened resin or the like, and is movably held within a complementary cylindrical cavity 50 in the end of the instrument body. A radial ange 54 on the head 52 is seated within an annular groove 56 formed in the wall of the cavity 50, and this serves to prevent endwise movement of the head 52 while permitting the latter to turn freely in the instrument body. Thus, when the head 52 is turned as by the use of a screwdriver (not shown) engaging a slot 60 in this head, the entire shaft 38 is turned.

As the shaft 38 is turned a movable contact device, 62, located within`the cavity 14 is moved between the ends 16 and 18 of that cavity through engagement of a spring-like U-shaped wire 64 with the thread 66 of the leadscrew or shaft 38 within the cavity 14. As indicated in the drawing, the contact device 62 includes a body member 68 formed out of metal so as to have a smooth groove 70 (FIG. 5) of substantially uniform cross-section, fitting against the threaded portion of the leadscrew. The ends of the resilient wire 64 are suitably attached as by welding or equivalent techniques to body member 68 in such a manner that the base 72 of the wire 64 lits and rides between next adjacent teeth of the thread 66 so as to resiliently engage the leadscrew and so hold the shaft 38 within the groove 70 and move the contact device longitudinally of the leadscrew as the latter is rotated.

A small contact means 74 or brush of a resilient character is provided, preferably formed integrally with the body member 68 as shown, and is constructed and arranged to resiliently engage the resistance element 20. The sides of the body member 68 are constructed and arranged as shown to t within grooves 76 (FIG. 6) formed in the sections 12-12 at the sides of cavity 14, in order to prevent rotation of the contact device 62 as the shaft 38 is turned. As the shaft is turned, the contact device 62 electrically connects the shaft 38 with the resistance element 20.

In order to complete the electrical circuit in the described FIG. 2 embodiment of potentiometer 10 a spring means or clip 78 having a bifurcated end 80 is disposed with its forked end within the cavity 46 and so arranged that the end 80 resiliently engages and presses against the flange 44 as shown, in order to hold shaft 38 against longitudinal movement of flange 44 away from abutment 47 and in order to establish electrical contact with the shaft.

Preferably the end is formed so that the pressur` against the flange 44 is applied equally on opposite sides o the shaft 38.

The clip 78 may conveniently serve as a terminal, ant for that purpose is illustrated as including an end 82 dis posed as shown and extending through a passage 84y t1 the outside of the potentiometer 10. This end 82 is pro vided with notches 86 (FIG. 3) which engage projection 88 formed on the mating surfaces of the housing sec tions 12, in order to securley latch the clip in place.

Those skilled in the art to which this invention pertain will realize that with the type of construction of the mov able device 62 illustrated in FIGS. 2, 5 and 6, danger o damage to the leadscrew and contact device fro-m exces sive leadscrew rotation is substantially eliminated. A the shaft 38 is turned to excess, forcing Contact device 61 against either of the ends 16 or 18 of the cavity, the wir 64 will spring up and snap over a portion of the tooth o thread 66 until such time as the direction of rotation o shaft 38 is terminated or reversed.r Reversal of rotatio: will in that event cause reversal of movement of devic 62. The construction of resilient clip 78 and the manne in which that member is used provides for effectivel locking the shaft 33 in place and preventing backlash.

In FIG. 7 of the drawing there is illustrated a modiiie embodiment of potentiometer 90 according to the pres ent invention. The modiied form of potentiometer ir cludes a body member having a non-conductive base 9 and a pair of upstanding ends 94 and 96. The potentiorr eter body portion including base 92 and ends 94 and 9 may be conveniently formed from a nonconductive mats rial such as a thermosetting phenolic resin, and is pre1 erably made of opposed complementary sections in accor with the construction shown in FIG. l, and so as to pr( vide a cavity adapted to be closed by a cover 9i Cover 98 may conveniently be of metal and formed as a inverted trough-like stamping of square U-shaped cross section, with pairs of aligned apertures in the side iiange for accommodation of respective tubular rivets 102, 10i all in a manner and form now well known in the ar Rivets 102 serve also to secure the complementary ser tions of the body portion together. Base 92 is forme to provide a set of grooves 104 and 106 located at th bottom of cavity 100. The groove 104 is formed and ai ranged to contain a U-shaped metal shorting strip 1! (FIG. 8), formed in accordance with known technique or as illustrated in Patent No. 2,886,681. The othf groove, 106, is adapted to contain a conventional wir wound resistance element 110.

At one side of each of the ends of the resistance elf ment there is located an end 112 of one or the othe of a pair of metal terminals such as terminal 114 show in FIG. 8. AEach of the terminals extends through tb base 92 by way of a respective groove 106 and passag 116, as indicated in the latter figure. The resistance el ment 110 is held in electrical communication with prt tuberances 118, one of which is formed on each of tk ends 112 of terminals 114, by means of tapered wedge -120. The construction of one of these wedges best illustrated in FIG. l0 of the drawing. It is ther shown that each of the wedges 120 has a curved top 12 and a llat bottom 124 and an intermediate curved, tapere wall portion 126. The wedges 120 are so constructed an used that the side edges 128 thereof engage a side of tf groove 106.

The wedges 120 are so formed that after the termina 114 and the resistance element 110 have been locate within the groove 106, the wedges can be driven int the positional disposition indicated, to firmly force tf ends of resistance element 110 against respective ones t terminals 114 and thus establish reliable electrical co1 nection between the terminals 114 and the ends of tl resistive means comprised in resistance element 110. Tf construction of the wedges 120 for the purpose indicate is extremely advantageous inasmuch as these wedges pr 'ent breaking or otherwise disrupting the resistance windng 130 on the resistance element 110. With prior contructions there has been a problem in satisfactorily esablishing reliable electrical termination of a resistance lement in this type of construction. Prior clips, etc., lave frequently been the source of a certain amount of Ireakage of resistance windings.

The ends 94 and 96 of the potentiometer body portion iovably support a metal shaft or leadscrew 132 which nay, as shown, extend to the exterior of the potentiomter. The shaft is formed and supported in a manner nd by means now well known in the art, and may be etained in position by conventional means such as a ansverse pin 150 that engages in a peripheral groove armed in the screw, or as indicated, for example, in atent No. 2,823,288. When shaft 132 is turned as by Je use of a screwdriver engaging a head 13d provided ierefor, a small, movable device 136 is moved longildinally in a selected direction along leadscrew 132, beween the inner faces of ends 94 and 96. As indicated in 1G. 9 of the drawing this movable device includes a on-conductive member 138 so formed as to have a nooth groove 140 of uniform cross-sectional contiguraon located th-erein. Groove 140 is preferably ot cross- :ction complementary to the outer periphery of thread 44. The sides of member 138 are constructed and aranged to slide in contact with respective sidewalls of avity 100, to obviate undesirable rotation of member 133 then shaft 132 is moved. A resilient U-shaped wire 142 imilar to the wire 64 previously described i-s attached to ody member 138 so as to engage the thread 144 of shaft 32. A contact means 146 is secured to member 138 and icludes one or more brush means 14S constructed and rranged to resiliently engage and electrically interconect the resistance element 110 and the strip 108. Prefrably there are at least two brushes comprised in brush leans 148, each of which brushes makes contact with a :spective one of the resistance element 110 and the strip 08. The resilient Wire 142 and the contact means 14:6 re attached to the body 138 by any of suitable known :chniques, and are so relatively constructed and arranged lat the wire 142 is insulated from the contact means 146.

While in the potentiometer illustrated in FIG. 7 a set E rivets 102, 102 may be employed to secure the housing :ctions together, other means may be employed. For Irample, a cementitious material may be employed; and t the embodiment illustrated in FIG. l an adhesive, or vets or clip means (not shown) may be employed to :cure the sections 12-12 together into a unitary struc- 1re.

Those skilled in the art to which this invention pertains ill realize that both o-f potentiometers 1) and 90 oper- :e in such a manner that it is virtually impossible to image these instruments by turning the shafts employed l them so as to Wedge or otherwise jam the movable )ntact device (62 or 136) employed in these instruments gainst either of the ends of the housing in which the )ntact device operates. Those skilled in the art will furier realize that any of the individual features of these )tentiometers shown can be used in a wide variety of fferently appearing electrical instruments. For these :asons the present invention is to be considered as being nited only by the appended claims.

We claim:

1. A screwshaft-operated potentiometer comprising:

first means, comprising housing means, forming a housing for containing operative elements of the potentiometer;

second means, comprising a screw-threaded shaft, supported by said first means and having a threaded portion of the shaft exposed in said housing;

third means, comprising a resistance element disposed in said housing with a portion presenting an exposed contact-face generally parallel to said screwshaft; and fourth means, comprising a contact device comprising a movable member formed with an elongate openended trough-like groove therein of depth no greater than the maximum radius of the thread of said shaft and disposed with a threaded portion of said screwshaft seated in said groove, said contact device cornprising spring-wire means having first and second ends secured to said member and a portion bridging said groove and said screwshait whereby to secure said member to said shaft and to yieidingly traverse said member along the screwshaft incident to rotation of the screwshaft, and said contact device comprising a Contact supported by said movable member and disposed to brush on said resistance element, said rst, second and third means also comprising means providing a plurality of potentiometer terminal means and means for completing a series electric circuit including a iirst one of said terminal means and a portion or" said resistance element and said contact and a second one of said terminal means.

2. A potentiometer as defined in claim l, wherein said contact device includes in said spring-wire means a U- shaped resilient metal Wire, the ends of said wire being attached to said body member adjacent one end of the latter, the base or" said U-shaped wire tting within the thread on said shaft adjacent the other end of the member so as to resiliently engage said shaft on a side thereof opposite the said groove.

3. A potentiometer as defined in claim 1, wherein said body member is formed of metal.

4. A potentiometer as deiined in claim 1, wherein said movable member is formed or a non-conductive material, and wherein said contact device and said spring-Wire means are insulated from one another.

5. A potentiometer which includes: a non-conductive housing having a cavity formed therein; means deiining parallel first and second grooves at the bottom of said cavity; an electrical return positioned within the first one of said grooves so as to extend into said cavity; a wirewound resistance eiement reposing in the second of said grooves so as to extend into said cavity; metal terminal members each disposed against a respective end of said resistance element at one side of said second groove, said metal terminal members being in electrical Contact with said resistance element; tapered wedges each having a substantially flat bottom, a curved top and a curved tapered Wall having side edges and connecting said top and said bottom, each wedge being positioned in said second groove with the top thereof located adjacent to the top oi said second groove, said wedges resiliently holding said resistance element against said terminal members, the side edges of said wedges engaging a side of said second groove; a threaded shaft positioned so as to extend through said cavity within said housing parallel to said resistance element; a non-conductive body member having a smooth groove of substantially uniform cross-sectional configuration formed therein, constructed and positioned so 'that said smooth groove tits in complementary disposltion against said shaft; a U-shaped metal wire spring attached to said body member and so disposed that each of the ends of said U-shaped metal wire is attached to said body member, and so disposed that said U-shaped metal wire extends across said shaft at the side thereof opposite said body member and resiliently engages the thread on said shaft in order to hold said body and shaft together with said shaft in said smooth groove; and contact means attached to said body member, said Contact means including brush means constructed and arranged to engage said resistance element and said electrical said contact means being insulated from said U metal wire spring.

6. A potentiometer as recited in claim l wherein there is included an improved means for making Contact with the ends of said resistance element, comprising a. conductive terminal at one end of said resistance element in contact therewith and extending external to said cavity,

return, -ohaped and a tapered wedge member driven into said housing adjacent to said one end of said resistance element and on the side opposite to that contacted by said conductive terminal and pressing said resistance element against said conductive terminal to insure better electrical contact between said resistance element and said conductive terminal, said tapered wedge member having a curved top end, a flat bottom end, and a curved tapered wall connecting said top and bottom.

7. In a potentiometer of the type having a housing wherein a threaded shaft is rotatably supported spaced from an elongate resistance means, and a contact device is operatively engaged with said threaded shaft and makes wiping contact with said resistance means incident t movement along the resistance means, an improved contact device comprising: a block of insulating material having a groove formed therein of depth no greater than the maximum radius of the thread of said shaft, for complementary sliding engagement with said threaded shaft, a U-shaped resilient metal wire extending generally longitudinally of said threaded shaft, said resilient wire having ends each attached to said block of insulating material adjacent a respective one of opposite sides of said groove and having its base bridging said groove and extending over said threaded shaft to t and engage the thread thereof and effective to resiliently hold said block of insulating material to said threaded shaft, and means, including a metal sliding contact carried by said block and constructed and arranged to extend toward said elongate resistance means and to make wiping contact therewith incident to movement of said block along said shaft. 8. A potentiometer having a housing defining a cavity containing a threaded shaft rotatably supported by said housing, an elongate resistance means spaced from said threaded shaft, and a contact device having a conductive body member having a portion of U-shape, the body member being constructed and arranged for slidably engaging said threaded shaft, said Contact device having two flanges, each extending away from said portion of U- shape at a respective one of the ends thereof, said housing having opposite walls adjacent said threaded shaft, parallel grooves each in a respective one of said opposite walls, each of said flanges respectively extending into a respective one of said grooves for providing guidance for said contact device as it is moved along said threaded shaft, a contact formed as part of said body member at said portion of U-shape and extending therefrom for engaging the elongate resistance means, and a resilient U-shaped spring extending generally parallel to a plane defined by the said flanges, said resilient U-shaped spring having each of its ends attached to a respective one of said flanges of said contact device and having its base bridging said portion of U-shape and extending over said threaded shaft to fit between teeth of the thread thereof and to resiliently hold said contact device to said threaded shaft.

9. A contact device for use in a variable resistor which resistor comprises an elongate resistance element and a screwshaft, the contact device being constructed and arranged for actuation by the leadscrew to make wiping electrical contact along said resistance element, said contact device comprising:

first means, comprising a body member formed with opposite side portions and an intermediate portion all of which portions are shaped to define a longitudinally-extending concave relatively smooth open groove of dimensions and configuration for complementary reception of a portion of a leadscrew and said groove being of depth no greater than the maximum radius of the thread of said screwshaft;

second means, comprising electrical contact means, supported by said body member and constructed and arranged for cooperation with an elongate resistance element to thereby make electrical contact therewith and to resiliently press said body member against a leadscrew;

and third means, comprising a single generally U shaped resilient wire member having two end por tions and a base portion interconnecting the end por tions, said end portions being each secured to sai body member on respectively opposite sides of Sai groove and disposed with said base portion bridgin said groove and constructed and arranged for engage ment with a leadscrew between next-adjacent tee't of the thread thereof for imparting motion along th leadscrew incident to relative rotation therebetweer and for holding said body member in close coopei ative engagement with such a leadscrew.

10. A contact device according to claim 9, said bod member consisting essentially of a deformed sheet-metz plate having opposed flanges, and said contact means con prising essentially a protruding resilient contact linger di pending from and integral with the plate, and said resilier wire member having the ends thereof extending throug respective apertures formed in said flanges and attache to said body member by fusion therewith.

1l. A contact device according to claim 9, said bod member comprising essentially a block-like body of ele trically insulative material, and said resilient wire membf having at least one end thereof embedded in the bloc] like body to securely attach the wire member to the boc' member.

12. In a variable resistor, the combination comprising first means, including an elongate resistance element i1 cluding a resistive means;

second means, including means forming a cavity 3 which the said elongate resistance element repose third means, comprising a terminal device, said term nal device being disposed at least in part in said cavi in contact with a portion of said resistive means;

and fourth means, comprising a resilient wedge co: structed and arranged at least in part in said cavi in contact with said resistance element and resilien ly forcing said terminal device and said resisti means into firm electrical contact each with the oth thereof.

13. In a variable resistor, the combination defined l claim 12, the said resistive means comprising a resistant wire.

14. For a variable resistor having a body, a resistant element in said body, and a rotatable screwshaft di posed parallel to the resistance element, the improveme comprising:

a contact device constructed and arranged to be su ported upon'and by the screwshaft for moveme therealong incident to rotation of the screwshaft, sa device comprising a body having a longitudinall extending portion formed to accommodate an arcua portion of the lower half of the periphery of a leng of the screwshaft, and said device comprising a sprii wire having rst and second ends secured to sa body and having intermediate said ends respecti` portions extending generally along said screwshz and a middle portion extending transversely of sa body and bridging said longitudinally-extending pc tions and arranged to engage in the groove of tl thread of the screwshaft and thereby hold the sa body to the screwshaft,

whereby said body when unrestricted may be traversl along the screwshaft by rotation of the screwshz and whereby incident to arrestment of the body fro longitudinal traverse along the screwshaft the mi dle portion of said spring wire yields to continu= rotation of the screwshaft without damage to t'. resistor.

15. A contact device for a screwshaft-operated variab resistor having a screwshaft and an elongate resistance el ment arranged parallel to the screwshaft, said device co1 prising:

a body member having upper and lower faces and co structed and arranged with an elongate shallow ope 9 ended groove longitudinally along the upper face thereof for reception therein of a portion of the lower periphery of a length of screwshaft;

spring wire means, having first and second ends firmly secured to said body member, and having an intermediate portion bridging said groove and arranged for thread-engagement with the upper surfaces of the screwshaft for securing the body member to the screwshaft and for sliding the body member along the screwshaft incident to rotation of the screwshaft; and

a contact carried by said body member and extending downwardly therefrom and arranged to contact and brush on the resistance element.

16. A potentiometer comprising, in combination with n elongate housing comprising a body and which housing orms an enclosure bounded by interior walls and in which housing are enclosed an elongate resistance element nd an elongate conductive strip, and an elongate lead- :rew supported by the housing and having an end accesible from the exterior of the housing for imparting rota- `.on to the leadscrew, and the leadscrew having a screw- Jreaded portion exposed within the interior of the hous- 1g:

a movable device including a non-conductive member having opposed portions disposed at opposite sides of the leadscrew and having at least one surface arranged to bear against one of said interior walls to prevent rotation of the device with the leadscrew incident to rotation of the leadscrew, said device comprising a resilient bent wire member secured to said non-conductive member and said wire having a single resilient portion extending transversely across the leadscrew and engaged in the groove of the thread of the leadscrew, and said movable device including contact means carried by said non-conductive member and comprising at least two resilient brush means each engaging a respective one of said conductive strip and said resistance element to electrically interconnect the conductive strip to a selected portion of the resistance element; and

terminal means connected to respective ones of said conductive strip and end portions of said resistance element;

whereby, incident to rotation of the leadscrew the said device is moved therealong to electrically connect said conductor strip with various portions of said resistance element until movement of said device is arrested and whereby when movement of said device is arrested continued rotation of said leadscrew induces slippage of said resilient portion of said wire over the rib of the thread to avoid damage to the potentiometer.

17. A potentiometer comprising:

first means, including means forming an elongate housing having at least one interior wall, said housing providing interior space for enclosing resistance element and conductive strip means;

second means, comprising an elongate resistance element disposed longitudinally of said housing and supported thereby and therein, said resistance element having a longitudinally-extending exposed surface within said housing, and said second means including terminal means including terminals connected to respective end portions of said resistance element;

third means, comprising an elongate conductive strip supported by said housing and disposed in said housing adjacent to said resistance element, and said third means comprising a terminal connected to said conductive strip;

fourth means, including an elongate leadscrew means supported by said housing and disposed substantially parallel to the exposed surface of said resistance element, said leadscrew means comprising a threaded portion having a helical rib the convolutions of which are separated by an intervening helical groove and lt) said leadscrew means having an end portion accessible from outside said housing to permit rotation of at least the said threaded portion; and

fifth means, comprising a movable device disposed in said housing and including a contact-carrying member having at least one portion disposed along said leadscrew and having at least one portion guided by contact with said interior wall tokobviate rotation of member with the leadscrew incident to rotation of the latter, said movable device further including a resilient wire supported by said contact-carrying member and carried thereby, said resilient wire having a resilient portion free to move relative to said member and said resilient portion including a portion of said wire extending transversely across and engaging said leadscrew and normally disposed in the said groove of the thread of the leadscrew between adjacent convolutions of the rib thereof, and said resilient portion being adapted to flex and permit the portion thereof engaging the leadscrew to ride over the said rib, and said fifth means comprising a contact carried by said contact-carrying member and insulated from said leadscrew, said Contact comprising brush means resiliently engaging and electrically interconnecting said conductive strip and said exposed portion of said resistance element;

whereby incident to rotation of said leadscrew said movable device is moved along said leadscrew until movement of the device is arrested and whereby said conductive strip is electrically connected to various longitudinally-spaced portions of said resistance element and whereby incident to arrestment of normal movements of said movable device with concurrent continued rotation of the leadscrew said portion of said wire engaging the leadscrew moves out of said groove and over said rib, thereby obviating damage to the potentiometer incident to arrestment of movement of said movable member.

18. A potentiometer according to claim 17, in which said contact-carrying member is electrically non-conductive and in which said resilient wire comprises a portion affixed to said contact-carrying member.

19. For a potentiometer of the type having a terminal and la rotatable lea-dscrew the rotation of which affects adjustment `of resistance exhibited at terminals of the potentiometer, a movable device adapted to be moved by rotation of the leadscrew, said movable device comprismg:

an electrically non-conductive member adapted to straddle the leadscrew and having portions adapted to be disposed at respective diametr-ically-opposite locations along the leadscrew, said member carrying electrically interconnected resilient brush means and having secured thereto a resilient bent wire having a first portion firmly secured to said member and a second portion connected to said first portion and free to be flexed, said wire having a third portion connected to said second portion and extending transversely across the leadscrew and adapted to engage in the groove of the thread of the leadscrew between successive convolutions of the rib `of the thread whereby incident to rotation of such leadscrew said member is moved along the leadscrew until such movement is arrested and whereby incident to arresting of said member during continuation of rotation of said leadscrew said third portion rides out of said groove and over said rib 0f the thread of the leadscrew to obviate damage.

20'. A leadscrew-adjusted variable resistor comprising:

first means, including an elongate housing having a body;

an elongate resistance element mounted in said housing;

a leadscrew rotatably supported by said housing and having a threaded portion exposed in said housing,

amarre 11 said leadscrew being arranged substantially parallel to said resistance element; slider arranged for movement along said leadscrew in said housing, said rst means comprising means preventing rotation of said slider around said leadscrew;

l?. Wire spring yielding zand snapping over the thread o the leadscrew as rotation of the leadscrew is con tinued to excess, and whereby said leadscrew' is in sulated from said Contact; and means providing electrical connections to said con tact and said resistance element.

a contact carried by said slider, said contact having a References Cited in the le of this patent UNITED STATES PATENTS portion in electrical Contact with said resistance element;

a bent wire spring, insulated from said Contact, carried 10 823,238 Boums et a1 Feb. 11, 195; by said slider, said bent Wire spring having a por- 2,360,217 Boums N0v 11, 1915: tion extending transversely across said leadscrew and 2,870,304 OBrian I an. 20, 1951 normally engaged in the groove of the thread of the 2,873,338 Elliott Feb. 10, 195! lleadscrevv whereby rotation of the leadscrew nor- 2,895,116 Morrison July 14, 195i mally induces movement of the bent Wire spring and 15 2,932,808 Bourns et al Apr, l2, 1961 the slider along the leadscrew, a portion of said bent 2,946,975 Caddook July 26, 196* UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 124,779 March 10, 1964 Richard E. Caddock et a1.

l It is hereby certified that errorvappears in the above numbered pai ent requiring correction and that the said Letters Patent should read as corrected below.

Column 10, line 44, for "affects" read effects Signed and sealed lthis 24th day of November 1964.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNE Attcstng Officer Commissioner of Paten 

20. A LEADSCREW-ADJUSTED VARIABLE RESISTOR COMPRISING: FIRST MEANS, INCLUDING AN ELONGATE HOUSING HAVING A BODY; AN ELONGATE RESISTANCE ELEMENT MOUNTED IN SAID HOUSING; A LEADSCREW ROTATABLY SUPPORTED BY SAID HOUSING AND HAVING A THREADED PORTION EXPOSED IN SAID HOUSING, SAID LEADSCREW BEING ARRANGED SUBSTANTIALLY PARALLEL TO SAID RESISTANCE ELEMENT; A SLIDER ARRANGED FOR MOVEMENT ALONG SAID LEADSCREW IN SAID HOUSING, SAID FIRST MEANS COMPRISING MEANS PREVENTING ROTATION OF SAID SLIDER AROUND SAID LEADSCREW; A CONTACT CARRIED BY SAID SLIDER, SAID CONTACT HAVING A PORTION IN ELECTRICAL CONTACT WITH SAID RESISTANCE ELEMENT; A BENT WIRE SPRING, INSULATED FROM SAID CONTACT, CARRIED BY SAID SLIDER, SAID BENT WIRE SPRING HAVING A PORTION EXTENDING TRANSVERSELY ACROSS SAID LEADSCREW AND NORMALLY ENGAGED IN THE GROOVE OF THE THREAD OF THE LEADSCREW WHEREBY ROTATION OF THE LEADSCREW NORMALLY INDUCES MOVEMENT OF THE BENT WIRE SPRING AND THE SLIDER ALONG THE LEADSCREW, A PORTION OF SAID BENT WIRE SPRING YIELDING AND SNAPPING OVER THE THREAD OF THE LEADSCREW AS ROTATION OF THE LEADSCREW IS CONTINUED TO EXCESS, AND WHEREBY SAID LEADSCREW IS INSULATED FROM SAID CONTACT; AND MEANS PROVIDING ELECTRICAL CONNECTIONS TO SAID CONTACT AND SAID RESISTANCE ELEMENT. 